Photoinhibition

Under photoinhibition , even light inhibition , refers to the inhibition of photosynthesis by high illuminance levels far above the light saturation point .

The causes of the photoinhibition lie in the energy oversaturation of the pigment system. The reaction center of photosystem II is particularly affected.

There, absorbed light energy is converted more strongly into heat, whereby the photoelectron transport is reduced. If this excess excitation energy cannot be emitted by the PS II, the excited chlorophyll preferably changes to the triplet state (= energy level of the π electrons of the chlorophyll achieved through heat release and electron spin reversal), which creates highly reactive singlet oxygen .

If these two states can no longer be intercepted by β-carotene or the xanthophyll cycle (conversion of the excess excitation energy into heat), the chlorophyll is photo- oxidized and thus inactivated.

Photoinhibition is particularly evident in plants with C3 photosynthesis in arid and subtropical areas (for example all types of fruit). These plants with their low photosynthetic potential, which are already saturated with low light irradiation, are particularly susceptible to photoinhibition.

On the other hand, C4 plants with a high photosynthetic potential, which is only saturated when there is relatively high light irradiation, can tolerate much higher light irradiation.

literature

• Ulrich Lüttge, Manfred Kluge, G. Bauer: Botany . 5th edition. Wiley-VCH, Weinheim 2005, ISBN 978-3-527-31179-8
• Gerhard Richter: Metabolic Physiology of Plants: Physiology and Biochemistry of Primary and Secondary Metabolism. Georg Thieme Verlag, 1998, ISBN 978-3-134-42006-7 . Box 3.14, page 136

Web links

• Photoinhibition. In: Spectrum Lexicon of Biology.